1. Field of the Invention
The present invention relates to wall-mounted load control devices for control of the power delivered from an alternating-current (AC) power source to an electrical load, and more particularly, to a mounting plate for a load control device having a means for grounding a metal faceplate.
2. Description of the Related Art
Typical load control devices are operable to control the amount of power delivered to an electrical load, such as a lighting load or a motor load, from an alternating-current (AC) power source. Wall-mounted load control devices are adapted to be mounted to standard electrical wallboxes. A dimmer switch comprises a controllably conductive device (e.g., a bidirectional semiconductor switch, such as, a triac), which is coupled in series between the power source and the load. The controllably conductive device is controlled to be conductive and non-conductive for portions of a half-cycle of the AC power source to thus control the amount of power delivered to the load (e.g., using a phase-control dimming technique). A “smart” dimmer switch (i.e., a digital dimmer switch) comprises a microprocessor (or similar controller) for controlling the semiconductor switch and a power supply for powering the microprocessor.
An electronic switch (i.e., a digital switch) comprises a controllably conductive device (such as a relay or a bidirectional semiconductor switch), a microprocessor, and a power supply. In contrast to a smart dimmer switch, the controllably conductive device of an electronic switch is not controlled using the phase-controlled dimming technique to variably adjust the intensity of a lighting load, but is controlled to be either conductive or non-conductive during each half-cycle of the AC power source to simply toggle the electrical load on and off. Digital dimmers and switches may further comprise occupancy detection circuits such that the dimmers and switches are able to operate as occupancy sensors to automatically turn on lighting loads in response to the presence of an occupant (i.e., an occupancy condition) and automatically turn off the lighting loads in response to detecting the absence of an occupant (i.e., a vacancy condition).
Such wall-mounted load control devices are typically installed with a faceplate. In the event that the faceplate is made of a conductive material (i.e., metal), the faceplate must be coupled to earth ground to comply with national electrical regulations. A prior art load control device typically comprises a yoke (or mounting plate) that is designed to be coupled to both the electrical wallbox and the faceplate. Typically, the yoke of such a prior art load control device is made of metal and further comprises a ground wire—coupled to the yoke—such that the metal yoke may be coupled to earth ground.
When such a prior art load control device is installed with a metal faceplate, the faceplate is coupled to earth ground because the faceplate contacts the metal yoke (either directly or through a faceplate screw, and the yoke is coupled to earth ground via the ground wire. Thus, because the faceplate (being made of metal) is electrically as well as mechanically coupled to the grounded metal yoke, national electrical regulations are properly satisfied.
However, metal yokes can be quite costly. Therefore, there exists a need for a load control device having a low cost grounding means for a metal faceplate—particularly, when the load control device comprises a yoke made of a non-conductive material.